1. Field of the Invention
The disclosure herein relates generally to the field of severing a tubular member. More specifically, the present disclosure relates to a method and apparatus for cutting downhole tubulars.
2. Description of Related Art
As is well known, hydrocarbon producing wellbores 2 are lined with tubular members, such as casing 4, that are cemented into place within the wellbore 2. Additional members such as packers and other similarly shaped well completion devices are also used in a wellbore 2 environment and thus secured within a wellbore 2. From time to time, portions of the casing 4 (or other tubular devices) may become unusable and require replacement. On the other hand, some tubular segments have a predetermined lifetime and their removal may be anticipated during completion of the wellbore 2. Because downhole tubulars are often secured to the wellbore 2, the tubular must be radially severed at some point along its length in order to remove it from the wellbore 2. Radially severing a tubular usually involves disposing a downhole tool 6, such as a tubing cutter, within the well bore 2 for cutting the tubular.
In FIG. 1, one example of a prior art device is illustrated. The downhole tool 6 can be supplied with an anchoring system 10 that anchors the tool 6 within the casing 4 prior to a cutting operation. Integral with the tool 6 often is a cutter mechanism 8 on which cutter blades 9 are attached. Actuation means associated with the downhole tool 6 are used for rotation of the cutting head where the cutting head includes cutting blades used for severing the casing 4. Once the casing 4 is severed, the portion of the casing 4 above the incision can be removed from within the well bore 2. Generally these downhole tools 6 are disposed within the well bore 2 via a wireline 12 extending from a surface truck 18 through pulleys 16. The wireline should be strung through a packoff head 14 at the surface to ensure sealing within the well bore 2. Examples of such cutting devices can be found in Bering, U.S. Pat. No. 1,358,818, Scherer et al., U.S. Pat. No. 3,859,877, and Hanna, U.S. Pat. No. 5,368,423.
However each of these devices suffer from one or more of the following disadvantages. For example, none of the devices in the above cited references have addressed the issue of how a cutter might respond to variations of material or material density in the material that is being severed. Often the casing, or other tubulars, can have inherent inconsistencies within the casing material causing the hardness and/or toughness of the material to vary at different spots along the circumference of the tubular. This can lead to the production of shock impulses within the cutting devices capable of damaging the device. Other disadvantages of these devices involve the cut itself. Many of these devices produce an uneven or irregular cut along the severed surface of the tubular. There are currently no provisions for producing an even and consistently cut surface along the severed area. Therefore there exists a need for a responsive casing cutter having the ability to produce consistent clean cuts along the circumference of tubular.